This includes possible aviation insurance losses totaling $6-15 billion, S&P said in a report.
Other specialty lines likely to be affected by the conflict include cyber, political risk and marine war insurance, S&P said.
The aviation market sees years of legal wrangling between lessors and insurers over planes trapped in Russia due to its invasion of Ukraine and subsequent Western sanctions.
The world's top aircraft lessor AerCap has submitted a $3.5 billion insurance claim for more than 100 jets stuck in Russia.
"We believe it may take many years to settle the ultimate losses incurred by aircraft leasing companies, insurers, and reinsurers," S&P said.
The top 21 global reinsurers rated by S&P will likely suffer around half of the overall losses, it said.
This would hit the earnings of most of them, while for "a few outliers" it could also hit their capital positions, given they also face large natural catastrophe losses already this year.
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